Antihunt electrical servomotor apparatus



Oct. 31, 1950 T. R. HARRISON.

mrmum muzcmxcm. SERVOMOTOR APPARATUS Filed March 25. 1944 4 Sheets-Sheet ,1

FIG.2

INVENTOR THOMAS R. HARRISON ATTC Oct. 31, 1950 v T. R. HARRISON 2,528,054

ANTIHUNT ELECTRICAL SERVOMOTOR APPARATUS Filed March 25, 1944 4 Sheets- Sheet 2 INVENTOR. THOMAS R.HARRISON ATTO EEEY.

Oct. 31, 1950 T. R. HARRISON 2,528,054

ANTIHUNT ELECTRICAL SERVOMOTOR APPARATUS 4 Sheets-Sheet 3 Filed March 25, 1944 INVENTOR. THOMAS RHARRISON ATTNEY.

Oct. 31, 1950 1', HARRISON 2,528,054

ANTIHUNT ELECTRICAL SERVOMOTOR APPARATUS Filed March 25, 1944 4 Sheets-Sheet 4 FIG.

FIG.|2

INVENTOR. THOMAS R HARRISON ATTOR Y.

Patented Oct. 31, 1950 ANTIHUNT ELECTRICAL SERVOMOTOR APPARATUS Thomas It. Harrison, Wyncote, Pa., assignor, by mesne assignments, to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application March 25, 1944, Serial No. 528,088

The present invention relates to automatic exhibiting and/or controlling systems, and particularly, to the elimination of the hunting tendency of such systems.

A general object of the present invention is to provide self-balancing exhibiting and/or controlling apparatus including novel and effective means for introducing an anticipating control action into the apparatus rebalancing operations so as to eliminate or at least substantially minimize the hunting tendency which inevitably re- 17 Claims. (Cl. 318-29) suits from failure to terminate the rebalancing operations promptly enough to compensate for the inertia of the moving components of the apparatus.

The present invention is of particular utility in self-balancing electrical networks of the potentiometric or Wheatstone bridge type in which rebalancing operations are rapidly effected as required by means including a reversible rotatable rebalancing motor. Such a motor has a tendency to coast or continue its rotation after being deenergized.

In accordance with the present invention, upon change in the magnitude of a measured or other controlling condition, a normally balanced electrical network becomes unbalanced and sets into operation a driving system for efiectuating a rebalancing adjustment of the network. Before completion of the rebalancing operation an additional electrical effect is created which causes premature deenergization of the driving'system, and if desired, energization of the driving system for operation in the reverse direction. This additional electrical efiect is correlated to the unbalance of the network in such manner that the driving system 'opgrates to rebalance the network in a minimum of time without the occurrence of overshooting of the balanced point of the network and consequent hunting.

Such anti-hunting provisions are desirable in self-balancing electrical networks inasmuch as the inertia of the various mechanically connected parts tends to so operate as to carry the driving system and its associated network rebalancing means beyond the true position of balance. 'When such over-shooting occurs, the network then becomes unbalanced in the opposite direction and initiates operation of the driving system in the reverse direction in an attempt to obtain rebalance, but again the necessary regulation is exceeded to thereby set up a continuous hunting about the balanced point.

The need for anti-hunting provisions in exhibiting and controlling apparatus or the self-' balancing type has long been recognized and various methods and structures have been proposed heretofore for supplying this need. For

example, it has preprosed to eliminate the hunting tendency by reducing the sensitivity of response. of the system to unbalance thereof, but such a solution is generally unsatisfactory because of the attendant reduction in the available power to pull the system into its exact condition of balance. One prior art method for eliminating the hunting tendency in such apparat'us is disclosed in Patent 1,827,520, issued to me on October 13, 1931. for Recording and ControlSystem and Apparatus Therefor, and reissued as Re. 21,309, in which the speed of rebalance of an electrical network is proportional to I the extent of network unbalance and mechanically movable means are provided to anticipate the true position of balance. Other prior art structures have provided means operative in response to the mechanical motion of the driving system for creating an electromotive force which is proportional to the speed of the driving system and which is opposed to the network unbalance to produce a condition of simulated rebalance of the network or a simulated condition of reverse unbalance before the network is actually rebalanced to thereby prematurely deenergize or to reverse the direction of energization of the driving system. As a result, the driving system is slowed down before the balanced position is reached and then gradually eases into the .balanced position without exceeding it.

A specific object of the present invention is to provide improved anti-hunting means for use in self-balancing exhibiting and controlling apparatus in which an effect is created in a simple and efficient manner by solely electrical means without reducing the sensitivity of response of the system to unbalance thereof and without involving the use of any physically movable parts whatever for terminating the rebalancing operation sufliciently prior to the attainment of rebalance as required to compensate for the inertia of i the driving system and associated rebalancing structure.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better under standing of the invention, however, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have asaaou illustrated and described a preferred embodiment of the invention.

Of the drawings: v

Fig. l is a diagrammatic illustration of a selfbalancing Wheatstone bridge network utilizing the invention;

Fig. 2 illustrates the mechanical details of the driving system and associated rebalancing structure of the arrangement of Fig. 1; I

Figs. 3 through 12 are fragmentary diagrams illustrating modifications f the arrangement of Fig. 1; and

Fig. 13 illustrates another type of self-balancing electrical network in which the advantageous features of the present invention may be incorporated.

In Fig. 1 of the drawings an arrangement including an electronic motor drive system designated generally by the numeral i and described in detail hereinafter is illustrated for producing eii'ects in accordance with the direction and extent of unbalance of a Wheatstone bridge network 2 which controls the operation of the electronic motor drive system i and is unbalanced in accordance with the variations in a quantity to be measured and/or controlled. Because of ,the small magnitude of the unbalanced electromotive .forces produced at the output terminals of the bridge network 2, it is not practicable, nor desirable, to have the said electromotive forces directly perform a measuring or controlling operation.

More specifically, an arrangement is illustrated in Fig. 1 for measuring and recording the temperature of a region in which a resistance thermometer bulb 3 is located. Bulb 2 comprises a coil of wire having a substantial temperature coemcient of resistance and is connected in one arm of bridge network 2. On change in the temperature to which bulb 2 is subjected, the bridge network I becomes unbalanced in one direction or the other and to an extent depending upon the direction and magnitude, respectively, of the temperature change.

Energizing current of suitable frequency is supplied the bridge network 2 from a source of alternating current through supply mains I and 5.

v'Io this end one pair of bridge conjugate points is connected by conductors 6 and l and a transformer to the supply mains 4 and 5. The other pair of bridge conjugate points constitutes the bridge output terminals and is connected by conductors 8 and 9 to the input terminals I 0 and H of the electronic motor drive system I. One of the last mentioned bridge conjugate pointsnis the point of engagement of a sliding contact i2 with a slidewire resistance II. The sliding contact I2 is adjusted along the slidewire resistance It in accordance with the variations in the temperature to which the bulb 2 is responsive by a structure shown by a dotted line in Fig. l but illustrated in detail in Fig. 2 and including a reversible electrical motor ll which is selectively energized for rotation in one direction or the other by the electronic motor drive system I. The remaining arm of the bridge network is comprised of a resistance It.

Upon variation in the temperature of the region to which the bulb 2 is exposed, the consequent change in resistance of the latter unbalances the bridge network 2 and as a result an unbalanced electromotive force will appear at the output terminals of the bridge network 2. This unbalanced electromotive force, the phase and amplitude of which is determined by the direction and extent of change of the temperature be ing measured, is impressed by conductors I and O on the input terminals of the electronic motor drive system I for selectively controlling the energization of the reversible motor H for rotation in one direction or the other, and hence, movement of the sliding contact II in the proper direction to reduce the bridge unbalanced electromotive force.

As is shown in Fig. 2, the shaft of motor ll drives a pinion I which is disposed in engagement with a gear ll. Attached to and movable with the gear I! is a pulley l8 around which is wrapped an endless cable ll. The cable II is connected to the sliding contact i2 so that when the motor rotates the contact I2 will be moved in one direction or the other to rebalance the bridge network 2. One end of the cable is runs over a pulley 20 which is pivotally mounted and biased by a spring 2| to take up the slack in the cable. The other end of the cable It runs around a stationary pulley 22.

A pen 23 is mounted on the carriage which carries the bridge rebalancing sliding contact l2 and is arranged in cooperative relation with a recorder chart 24 to thereby provide a continuous record of the adjustments of the sliding contact I2 which are required to keep the bridge network balanced, and hence, to provide a record of the variations in magnitude of the temperature to which the bulb 3 is subjected. The chart 24 is a strip chart and is arranged to be driven in any convenient manner, as for example, by a unidirectional motor 2! through suitable gearing, not shown, so that a record of the variations in the unknown temperature will be recorded as a con tinuous line on chart 24.

The electronic motor drive system I is conand 29 contain two triodes within the same envelope or bottle. The pre-ampliiler tubes 21 and 28 provide three stages of preampliflcation. It will be understood as the description proceeds, however, that more or fewer stages of pre-amplification may be employed as is desired.

Transformer 2! is provided with a primary winding 30 and a secondary winding 3|. The in-.- put terminal I0 of the electronic motor drive system is connected to one end of primary winding 3| and the input terminal II is connected to the other end thereof. Hence, the unbalanced alternating electromotive forces which are created at the output terminals of bridge network 2 upon change in the magnitude of resistance 2' are impressed on the transformer primary winding Ill and induce corresponding electromotive forces in the secondary winding 3|. The electromotive forces so created in secondary winding 2| are amplified by means to be described and including the pre-amplifler vacuum tubes 21 and 20 and the amplified quantity is utilized to control the operation of the motor drive tube 29 as required to effect selective energization of motor H for rotation in one direction or the other according to the phase of the said induced electromotive forces. To this end the motor H is provided with a pair of terminals 32 and 23 which are connected in the output circuits of the two triodes contained in'vacuum tube 28, and a pair of termlnais 24 and II which are connected to the alter-- hating current supply mains 4 and 5 through a condenser 38.

Motor i4 is a two phase rotating field motor and comprises a rotor 31 and two pairs of oppositely disposed field poles on one pair of which a winding 38 is wound and on the other pair of which a winding 39 is wound. Winding 38 ha its terminals connected to the motor terminals 34 and 35 and is supplied with energizing current from the alternatin current supply mains 4 and 5 through the condenser 38. Because of the inclusion of condenser 38 in the energizing circuit of winding 38, the current flow through this winding will be in phase with the voltage of the alternating current supply mains 4 and 5. The winding 39 has its terminals connected to the motor terminals 32 and 33 and is supplied with energizing current from the output circuits of the two triodes of the vacuum tube 29. The current supplied to the winding 39 from the vacuum tube 29 either leads or lags by approximately 90 the voltage of the alternating current supply mains and establishes a field in the motor rotor 31 which is displaced 90 in one direction or the other with respect to that established therein by the winding 38. The reaction between the field set up by the winding 39 with that set up with the winding 38 establishes a rotating field in the rotor which rotates in one direction or the .other depending upon whether the winding 39 is energized with current which leads or lags the voltage supplied by the supply mains 4 and 5, and consequently in accordance with the direction of unbalance of the bridge network 2. The direction and duration of rotation of the motor I4 is controlled in accordance with the direction and extent of unbalance of the bridge network 2 so that on rotation of the motor M the sliding contact I2 is adjusted in the proper direction to rebalance the bridge network 2.

. The amplifying tube 21 of the electronic motor drive system includes two heater type triodes designated by the reference characters 48 and 4| within the same envelope. The triodes 48 and 4| each include anode, control electrode, cathode, and heater filament elements. The heater filaments are connected in parallel and are supplied with energizing current from the secondary winding 42 of a transformer 43 having a line voltage primary winding 44 and additional windings 45 and 48. In order not to complicate the drawing the conductors connecting the transformer secondary winding 42 to the heater filaments of triodes 48 and 4| have not been shown. The transformer secondary winding 42 is also connected, by conductors not shown, to the heater filaments of the triodes contained within the amplifying tube 28 and the motor drive tube 29.

The electronic tube 28 also includes two heater type triodes designated by reference numerals 41 and 48 within the same envelope. Each of the triodes 41 and 48 include anode, control electrode, cathode, and heater filament elements. The heater filaments of triodes 41 and 48 are also connected in 7 parallel. The triode 48 is utilized as a half wave rectifier to provide a source of unidirectional voltage for energizing the anode or output circuits of the triodes 48, 4| and 41. To this end, the control electrode and cathode of the triode 48 are directly connected to each other, and the output circuitthereof is energized by the transformer secondary winding 45 through a circuit which may be traced from the left end terminal of the winding 45 through a conductor 49 to the anode of triode 48, the cathode thereof,

and through a conductor 58 to the positive terminal 5| of a filter generally designated by the reference character 52. 53 of the filter is connected by a conductor 54 to the right end terminal of the transformer secondary winding 45 and is also connected to ground potential through a conductor 85.

The filter 52 includes a condenser 55 which operates to smooth out the ripple in the output voltage of the filter between the points 5| and 53 and also includes a resistance 58 and a condenser 51 which operate to smooth out the voltage between the filter points 58 and 53. A further resistance 59 and a condenser 88 are provided in the filter 52 to smooth out the voltage between the filter points 8| and 53. Thus, the filter comprises three stages. A three-stage filter is provided because in order to obtain the most satisfactory and efiicient operation it is desirable that the voltage applied to the output circuit of triode 48 be substantially free from ripple whereas it is not necessary to supply anode voltage so completely free from ripple to the output circuit of the triode 4|. Likewise, it is not necessary to supply anode voltage so free from ripple to the output circuit of triode 41 as it is to triode 4|.

The anode or output circuit of the triode 48 may be traced from the filter point 8| comprising the positive terminal of the unidirectional voltage supply through a fixed resistance 62 to the anode of triode 48, the cathode, and through a cathode biasing resistance 63 shunted by a condenser 64 to the negative filter point 53 through the grounded conductor 85. The cathode biasing resistance 63 and condenser 64 are provided for biasing the control electrode of triode 48 negatively with respect to the cathode.

The input circuit of the triode 48 may be traced from the cathode through the parallel connected resistance 83 and condenser 84 and through the transformer secondary winding 3| to the control electrode. A tuning condenser 88 may desirably be connected in shunt to the transformer secondary windin 3| as shown.

The output circuit of triode 48 is resistancecapacitance coupled to the'input circuit of triode 4| by means of a condenser 61 and a resistance 68. Specifically, the anode of triode 48 is connected by condenser 81 to the control electrode of triode 4i and the control electrode of triode 4| is connected through the resistance 68 to the grounded conductor 85. The cathode of triode 4| is directly connected to the grounded conductor 85. The resistance 68 in addition to its coupling function serves to limit the extent to which the control electrode of triod 4| may go positive with respect to its associated cathode and also maintains the control electrode of triode 4| at the same potential as its associated cathode when no voltage is produced in the transformer secondary winding 3|.

The anode or output circuit of the triode 4| may be traced from the positive terminal 58 of the filter 52 through a fixed resistance 69 to the anode of triode 4|, the cathode, and the grounded conductor 85 to the negative terminal 53 of the filter.

The output circuit of triode 4| is resistancecapacitance coupled to the input circuit of the triode 41 by means of a condenser 18 which is connected between the anode of triode 4| and the control electrode of the triode 41 and by means of a resistance H which is connected between the control electrode of triode 41 and the cathode thereof. Th resistance H serves to lim- The negative terminal 7 it the extent to which the control electrode of the triode I! may be driven positive with respect to its associated cathode and also to maintain the said control electrode at the same potential as the cathode when no voltage is produced in the transformer secondary winding 3!.-

The electronic tube 29 includes two heater type triodes l2 and 13 within the same envelope. Anode voltage is supplied the output circuit of the triode 12 from the transformer secondary winding 46 through a circuit which may be traced from the left end terminal of the secondary winding 48 to the anode of triode 12, the cathode thereof,

a cathode biasing resistance 14 shunted by a condenser 15, a conductor 16 and motor winding 39 to the center tap on the transformer secondary winding 46. A condenser 11 of value suitable for tuning the motor winding 39 is connected in parallel to the latter. 7

Anode voltage is supplied the triode 13 through a circuit which may be traced from the right end terminal of the transformer secondary winding 46 to the anode of triode I3, the cathode, a cathode biasing resistance 8! shunted by a condenser 82, conductor 16 and motor winding 39 to thecenter tap on winding 46.

The cathode biasing resistances H and 8| and associated condensers l and 82 operate in a manner explained in detail hereinafter to effect premature deenergization of the motor H for rotation when the bridge network 2 18 being rebalanced following unbalancing thereof to anticipate the approach of the rebalancing contact I! to the true balanced position in order that the speed of the reversible motor H may be as great as possible during the rebalancing operation of the bridge network 2 without overshooting of the balance point and consequent hunting occurring. Preferably, the time constant of the parallel connected resistance 14 and condenser 15 is the same as that of the resistance 8! and condenser 82. To this end the resistances H and 8| may desirably be of the same value and so may the condensers l5 and 82.

The output circuit of the triode 41 is resistancecapacity coupled to the input circuits of the triodes I2 and 13 by means of a condenser 18 and a resistance 19. In particular, the anode of the triode 41 is connected through the condenser 18 and a current limiting resistance 83 to the control electrode of the triode l2 and through the condenser 18 and a current limiting resistance 84 to the control electrode of triode 13. Both of the said control electrodes are connected through their respective current limiting resistances 83 and 84 and the resistance 19 to the grounded conductor 65. A contact 80 in adjustable engagement with the resistance 19 is provided for varying the point of connection of the control electrodes of triodes 12 and 13 to th resistance I9.

The resistance l9and contact 80 perform a dual function, namely, to maintain the control electrodes of the triodes I2 and 13 at the same potential as th grounded conductor 85 when no voltage is induced in the transformer secondary winding 3 I and upon the induction of a voltage in the winding 3| to permit the flow of grid current to thereby limit the extent to which the control electrodes of the triodes l2 and 13 may go positive with respect to their associated cathodes.

The motor I4 is preferably so constructed that the impedance of the winding 39, when connected across the condenser 11, is the proper value to match the impedance of the anode circuits of the triodes l2 and 13 when the motor is operating, in order to obtain the most eiilcient operation. Preferably, the motor is so constructed that it has a high ratio of inductive reactance to resistance, for example, of the order of 6 to l or from 8 to 1 at the frequency of the energizing alternating current supplied to it. This provides for efficient action and power during the running condition of the motor with the least amount of heating and also provides a. low impedance path which provides a desirable braking action. v

The condenser 36 connected in the energizing circuit to the motor winding 38 is so selected with respect to the inductance of the latter as to pro vide a. series resonant circuit having a unity power factor. By virtue of the series resonant circuit, the total impedance of the motor winding 38 is substantially equal to the resistance of the winding, and since this resistance is relatively low a large current flow through the motor winding 88 is made possible. This permits the attainment of maximum power and torque from the motor H. In addition, the current flow through the motor winding 38 is in phase with the voltage of the alternating current supply mains l and I because of the series resonant circuit. The voltage across the motor winding 38, however, leads the current flow by substantially 90 because of the inductance of the winding 38.

Energizing current is supplied to the motor winding 39 from the transformer secondary winding 46 through the anode circuits of the triodes i2 and 13 through the circuits previously traced. The condenser 11 which is connected in shunt to the motor winding 39 is so chosen as to provide a parallel resonant circuit with the motor winding 39 having substantially unity power factor. This parallel resonant circuit presents a relatively high external impedance and a relatively low local circuit impedance. The relatively high external impedance is approximately the same as the impedance of the anode circuits of the triodes l2 and I3, and therefore, provides efiicient operation. The relatively low internal circuit impedance approximates the actual resistance of the motor winding 38, and since this resistance is relatively low the impedance of the local circuit is also relatively low.

For the condition when the bridge network 2 is balanced, no voltage is induced in the transformer secondary winding 3i, and hence, the potentials of the control electrodes of all of the triodes 40, 4|, 41, 12 and 13 remain substantially constant. Under this condition of operation a pulse of unidirectional current flows through the anode circuits of the triode 12 to the motor winding 39 from the left hand section of the transformer secondary winding 46 during the first half cycle of the alternating voltage supply. During the second half cycle of the alternating voltage supply a pulse of unidirectional current flows through the anode circuit of the triode 13 to the motor winding 39 from the right hand section of the transformer secondary winding 46. Since the control electrodes of the triodes 12 and 13 are connected together, and inasmuch as the potentials of these control electrodes remain substantially constant when the bridge network 2 is balanced, pulses of equal magnitude flow in the anode circuits of the triodes 12 and 13 during alternate half cycles of the alternating voltage zisipplied by the transformer secondary winding Consequently, when the bridge network 2 is balanced, pulsating unidirectional current of twice the frequency of the alternating supply current is impressed on the metawinding 3!. when thus energized,thcmotormtor3lismturged to rotation in either direction and remains stationary. Due to the relatively hi h direct current component of the current then flowing through the motor winding 3! a damping eflect isexertedontherotor3loithemotororincther words an eflect tending to retard rotation of the rotor 31. By virtue 01' this damping eiicct, it the rotor 31 hadbeen rotating currents are induced in the conductors of the rotor dissipating the rotors energy and thereby stopping its rotation.

Upon unbalance of the bridge network 2, the magnitude of the pulses of current flowing in the anode circuit of theiriode I! will be increased while the magnitude of the pulses of current flowing in the anode circuit of the triode I3 will be decreased. Consequently, the pulses of unidirectional current supplied to the motor winding 39 during the first half cycle will predominate over those supplied the motor winding 38 during the second half cycle. Such energization of the. mo-

tor winding 39 operates to introduce therein an alternating component of current 01' the same frequency as that supplied by the alternating current supply mains 4 and 5. This alternating component of current will be either 90 out of phase or 270 out of phase with the alternating current flowing through motor winding 38 depending upon the direction of bridge network unbalance and produces an alternating magnetic field in the motor core structure which reacts with the alternating magnetic field established by the motor winding 38 to produce a rotating field in the rotor 31. This rotating field rotates in one direction or the other depending upon the direction of bridge network unbalance and actuates the rotor 31 for rotation in a corresponding direction. When the motor winding 39 is so energized, the direct current component of current is decreased with the result that the rotor damping efi'ect is also reduced.

In order to obtain rapid operation of the reversible electrical motor M in efiectuating rebalance of the bridge network 2 without overshooting and consequent hunting taking place, the response of the motor II is correlated with the unbalancing and the rebalancing operations of the bridge network. This is accomplished by adjusting the contact 83 along the resistance I! which is employed for the purpose of coupling the output circuit of the triOde 41 to the input circuits of the triodes I2 and 13. By moving the contact 80 in an upward direction the amplitude of signal on the control electrodes of triodes I2 and I3 is increased for any given signal produced in the transformer secondary winding 3|, and by moving the contact 8|! in a downward direction, the amplitude of signal is decreased. This, therefore, adjusts the sensitivity of the electronic motor drive system I whereby the response of the reversible electrical motor ll may be correlated exactly with the operation of the bridge network 2. It will be apparent that, if desired, this sensitivity adiustment may be provided between two of the pre-amplifier stages instead of between the pre-amplifier and motor drive tubes. For example, the point of connection of the control electrodes of triode 41 to the resistance II may be made adjustable to provide such a sensitivity adjustment.

In some applications of the sell-balancing Wheatstone bridge network disclosed in Fig. 1, the damping action obtained as a result of the 10 direct current component of current through the motor winding 39 is suflicient to prevent overshooting and consequent hunting occurring. There are many other applications, however, whereinit is desired to effectuate the rebalanchigher rate of speed while maintaining a high degree of sensitivity and large driving torque even with a small driving signal impressedon the input circuit of the electronic system I, and in such applications the damping action obtained by means of the direct current component through the motor winding 39 is insuflicient to prevent coasting and consequent hunting occurring. In order that the speed of the reversible motor ll may be increased so as to fulfill the conditions of such high speed applications without overshooting and consequent hunting occurring, the cathode biasing resistances It and BI and their respectively associated condensers I5 and 82 have been provided in accordance with the present invention to cause premature deenergization oi the motor for rotation when the bridge network is being rebalanced as is required to compensate for the inertia of the motor rotating elements and the associated rebalancing means. The manner in which the resistances "and BI and condensers I5 and 82 operate to accomplish this result will now be explained.

As has been previously noted, unbalance oi the bridge network 2 produces an alternating electromotlve force of supply line frequency which is amplified by the pro-amplifier tubes 43, II and 41 and is impressed on the control electrodes of both motor drive tubes I2 and I3. On the assumption that the direction of bridge network unbalance is such that the alternating volttage impressed on the control electrodes of tubes I2 and I3 drives the said control electrodes in the positive or less negative direction during the half cycle of the supply line voltage that the anode of tube I2 is positive and the anode of the tube I3 is negative, and drives the control electrodes in the negative direction during the half cycle that the anode of tube I3 is positive, the conductivity of tube I2 will be increased by the bridge network unbalance while the conductance of tube 13 will be decreased. This difference in the conductivities of the two motor drive tubes operates to cause selective energizetion of the reversible motor M for rotation in the proper direction to effectuate rebalance of the bridge network 2.

when the alternating voltage impressed on the control electrodes of tubes I2 and I3 is sustained, there is a decrease in the conductance of tube I2 which is produced as the condenser I5 gradually charges to the new increased voltage drop across the biasing resistance 14 which is produced as a result of the increased conductance of tube I2. Simultaneously, there is an increase in the conductance of tube I3 which is produced as the condenser 82 gradually discharges to the new decreased voltage drop across the biasing resistance 8| which is caused by the decreased conductance of tube I3. stated differently, with sustained unbalance of the bridge network in one direction, there is an increase in the negative bias which is impressed on the control electrode of tube I2 and a decrease in the negative bias which is impressed on the control electrode of tube I3. With such bias voltages temporarily maintained on the input circuits of tubes 12 and I3 by virtue-oi the action of condensers I5 and 82, reduction in the degree of bridge network unnetwork unbalance is reduced to zero.

asaaou balance will abnormally decrease the conductivity of tube 12 and simultaneously increase that of tube 13. Due to this action equality in the conductivities of the two tubes 12 and It will be restored before the bridge network is completely rebalanced, and the conductive conditions of the tubes may even be reversed before the bridge network is rebalanced when the alternating voltage impressed on the input circuits of tubes 12 and 19 decreases at a suitably rapid rate in relation to the instantaneous magnitude of that voltage. Consequently, beforethe bridge network 2 has been rebalanced the energization of motor l4 for rotation in the rebalancing direction will have been reduced to zero and may even be reversed. This sequence of events brought about by the inclusion of the cathode biasing resistances 14 and ti and condensers l and 92 in the motor drive stage of the electronic motor drive system I produces a positive and powerful braking action which will quickly check the motor speed before the new balanced position of the rebalancing contact i 2 along the slidewire resistance I3 is reached, and which will gradually reduce the motor speed to zero as the bridge In this manner, the speed of operation of the reversible electrical motor l4 in eifecting rebalance of the bridge network 2 may be made exceedingly great without overshooting and consequent hunting taking place.

Upon sustained unbalance of the bridge network in the opposite direction, the conditions are reversed, that is, there is a decrease in the negative bias which is impressed on the control electrode of tube 12 and an increase in the negative bias which is impressed on the control electrode of tube 13 with the resulting retarding effect on the motor rotation as the bridge network balanced point is approached.

In Figs. 3 through 12, I have illustrated, more or less diagrammatically, fragmentary diagrams of advantageous modifications of the motordrive stage disclosed in Fig. l and including tubes 12 and 13.

The arrangement of Fig. 3 is generally like that of Fig. 1 but difiers therefrom in that it includes a cathode biasing resistance 85 and parallel connected condenser 86 which are common to both of the input circuits of the motor drive tubes 12 and 13. Specifically, the resistance 85 and condenser 86 are connected between the negative terminals of the damping components l4, 75, ill and 82 and the grounded conductor 65. Hence, the resistance 85 and condenser 89 constitute a 'mutual biasing means for the tubes 12 and 13 for effecting operation of the latter over an optimum portion of their grid voltage-plate current characteristic curves.

In the modification of Fig. 4 a single time delay or damping condenser 81 is employed in placeof the two time delay or damping condensers i5 and 82 of Fig. l. Condenser 91 is connected directly between the cathodes of tubes 12 and i9 and operates, in com'unction with resistances i4 and BI, upon sustained unbalance of the bridge network 2, to effectuate a delayed decrease in the conductance of the tube 12 or 13, the conductance of which was increased as a result of the bridge unbalance, and a delayed increase in the conductance of the other tube. As the rebalancing action of the reversible motor l4 and the associated rebalancing mechanism reduces the. unbalance of bridge network 2, delayed recovery in the biasing potentials across resistances i4 and 12 II is caused by the condenser I! to effect premature restoration of the tube conductances to equality or even a reversal in the conductive conditions, thus producing a positive and powerful damping action.

In the modification of condensers 99 and 99 are employed between the output circuit of the pre-amplifler tube 41 and each of the input circuits of the motor drive tubes 12 and II in place of the single coupling condenser 19 of Fig. 1. The coupling condensers 98 and 99 are so arranged and utilized that they also serve to accomplish the desired time delay or damping action provided by the condensers II and 82 of Fig. 1. Hence, there is no need for the condensers 15 and 92 in Fig. 5. v

Specifically, the anode of pre-amplifler tube 41 is connected to the common terminal of condensers 99 and 99. The other terminal of condenser 99 is connected through a current limiting resistance 93 to the control electrode of tube 12 and the other terminal of condenser 99 is connected through a current limiting resistance 84 to the control electrode of tube "I9. A pair of series connected cathode biasing resistances II and 9| are provided in the cathode circuit of tube 12 between the cathode and the grounded conductor 65, and a pair of similar series connected cathode biasing resistances 92 and 99 are provided in the cathode circuit of tube 19 between the cathode and conductor 55. A resistance 94 is connected between the control electrode of tube 12 and the point of engagement of resistances 92 and 93 in the cathode circuit of tube 19, and a resistance 95 is connected between the control electrode of tube 13 and the point of engagement of the resistances and 9| in the cathode circuit of tube 12. Resistances 94 and 95 serve in conjunction with their respectively associated resistances 99 and 9| to limit the extent to which the control electrodes of the tubes 12 and 13 may be driven positive with respect to their associated cathodes and also to maintain the said control electrodes at the same, potential as the cathode when the bridge network 2 is balanced. Thus, in this modification, the resistances 94 and 95 in conjunction with the resistances 9| and 93 serve to replace the resistance 19 of Fig. l. and accordingly, the desired sensitivity adjustment may be obtained by providing a variable coupling between stages of the pre-amplifier as previously explained.

In the arrangement of Fig. 5 the resistances 94 and 95 may be made very high in value in comparison to the highest permissible value of resistance 19 in Fig. l, and therefore, the same time delay or anti-hunting effect may be obtained with condensers 98 and 89 of small value compared to the value of condensers l5 and 82 of Fig. 1.

Each of the modifications of Figs. 6 through 12 is provided with a separate pair of triodes 9i and 91 between the output circuit of the preamplifier triode 41 and the input circuits of the motor drive tubes 12 and i3 and include resistsince-capacitance means in the anode circuits for producing premature deenergization of motor l4 or even reversal in the energization thereof during the bridge rebalancing operations as required to compensate for the inertia of the motor and associated rebalancing mechanism.

Referring to Fig. 6 it will be noted that the triodes 96 and 9'! are of the indirectly heated type having heater filaments which conveniently may be supplied with energizing current from the transformer secondary winding 42 of a trans- Fig. 5 separate coupling" 13- I former 99a which corresponds generally to the transformer 99 of Fig. 1 but includes an additional center tapped secondary winding 99 which is provided to supply energizing voltage to the anode circuits of triodes 96 and 91. The anode circuit of triode 96 may be traced from the left end terminal of winding 96 through a parallel connected resistance 99 and condenser I99 to the anode oi triode 96, the cathode thereof, a cathode biasing resistance I9I and a conductor I92 to the center tap on winding 96. The anode circuit or triode 91 may be traced irom the right end terminal through a parallel connec I99 and a condenser I99 to the an of triode 91, the cathode, a cathode biasing I96, and the conductor II! to the center tap on winding 98. V

The output circuit of the pre-ampliiler output triode 91 is coupled to the input circuits of triodes 96 and 91, which input circuits are-connected in parallel, by means of a condenser I96 and a resistance I91. To this end, the anode of triode 91 is connected through the condenser I99 to each of the control electrodes of triodes 96 and 91, and the said control electrodes are connected through the resistance I91 to the grounded conductor-66. Desirably, a current limiting resistance 69a may be connected between the control electrode of triode 96 and'the condenser I96, and a current limiting resistance 89:: may be connected between the control electrode of triode 91 and condenser I96. Thepoint of connection of the control electrodes of tubes 96 and 91 to the resistance I91 may be made adjustable, ii desired, for obtaining a sensitivity adjustment, or such adjustment can be provided between stages in the pre-amplifier as previously explained.

In Fig. 6 the cathodes of the motor drive tubes 12 and 13 are directly connected to each other and through a common cathode biasing resistance I99 and parallel connected condenser I 96a to the grounded conductor 65. The control electrode oi 14 plained. On the assumption that the directidfl of bridge network unbalance is such that the alternating voltage impressed on the control electrodes of triodes 96 and 91 from the output stage of the pre-amplifler drives the said control electrodes less negative or even positive during the halt cycle of the supply line voltage that the anode of triode 96 is positive and the anode of triode 91 is negative, the conductivity of triode 96 will be increased while that of triode will be decreased. Consequently, the pulsating potential drop produced across resistance I9I by tube 12 is connected directly to the cathode of a,

triode 96, and the control electrode of tube 19" is connected to the cathode of triode 91. Hence, the pulsating potential drop produced across the resistance I9I by the current flow through triode 96 is utilized to control the conductivity of tube 12 and the pulsating potential drop produced .across the resistance I95' by the current flow through triode 91 is utilized to control the conductivity of tube 13. The pulsating potential drop across each of the resistances I9I and I95 isoi the proper polarity to tend to drive the associated control electrodes of tubes 12' and 13 positive with respect to the potentials of the cathodes of said tubes.

It is noted that when tubes 12 and 19 are of the type which cut of! when thecontrol electrodes are at the same potential-as the associated cathodes, resistance I98 and the parallel condenser I96a may be eliminated. For tubes requiring negative bias for cut oil, the conduction of one tube 12 or I3 stores a potential across the condenser I96a which serves as bias to cut of! the other tube.

The manner in which theparallelconnected resistance 99 and condenser-I99, and the parallel connected resistance I93 and condenser I99 in Fig. 6 operate to prematurely deenergize the motor I9 for rotation or to energize the motor ,for rotation in the reverse direction during the bridge rebalancing operations as req'uired'to compensate for the inertia of the motor and associated rebalancing mechanism will now be exthe current flow through triode 96 will exceed that produced across resistance I96 by the current flow from triode 91. This will cause the conductivity of tube 12 to exceed that of tube 19, and accordingly, selective energization of motor I9 for rotation in the proper direction to eflect' rebalance of the bridge network 2.

The increased conductivity of triode 96 will cause an increase in the potential drop across resistance 99 and condenser I99 in its anode circuit, and similarly, the decreased conductivity of triode 91 will cause a decrease in the potential drop across the resistance I93 and condenser I99. Because of the tendency of the condensers I99 and I99 to delay any change in potential drop across their terminals, the said changes in potential drop across resistances 99 and I 99 are gradual and occur at a rate determined by the time constants of the parallel connections. The effect of such gradual increase in potential drop across resistance 99 is a gradual reduction in the anode voltage impressed on the triode 96 during the half cycles that the latter is conductive, and similarly, the efiectof the gradual decrease in potential drop across resistance I93 is a gradual increase in the anode voltage impressed on the triode 91 during the conductive half cycle of the latter. This action effectively decreases the amplification provided by triode 96 and increases ,that of triode 91 with the result that before the bridge network 2 has been rebalanced the pulsating potential drop produced across resistance I95 is made equal to or greater than the potential drop across resistance I9I. As a result, the

, motor I9 will be deenergized for rotation or energized for rotation in the reverse direction before bridge rebalance has been accomplished. By proper choice of the circuit components, this premature deenergization of motor I9 or reversal in ene'rgization may be accomplished as required to exactly compensate for the inertia of the motor and its associated rebalancing mechanism, thus efiectively eliminating or at least minimizing overshooting and consequent hunting. As the motor speed gradually decreases, the potentials across the condensers I99 and I99 equalize so that when the motor hascome to a stop and the unbalanced voltage has been reduced to zero, the motor is not energized for rotation in either direction and remains stationary.

The arrangement of Fig. 7 is generally like that of Fig. 6 but differs therefrom in respect to the manner of coupling the output circuits of the triodes 96 and 91 to the input circuits of tubes 12 and 'I3. In Fig. 7 the transformer 93b corresponds to the transformer 93a of Fig. 6 and difi'ers therefrom in that two separate secondary windings I99 and I I9 are provided in place or the winding 98. The anode circuit of triode 96 is energized by the winding I99 through a circuit which may be traced from the right end 01 winding I99 to the anode of triode 96, the cathode, a

end terminal of winding I00.

cathode biasing resistance I I I, the grounded conductor 00, a resistance H2, and the parallel connected resistance and condenser I00 to the left Similarly, the anode circuit of triode 01 may be traced from the left end terminal of winding IIO to the anode of triode 01, the cathode biasing resistance III, grounded conductor 00, a resistance II I, and the parallel connected resistance I03 and condenser I04 to the right end terminal oi winding I ll.

The cathodes of the motor drive tubes in this modification are directly connected to each other and to the grounded conductor 50. The control electrode oi tube 12 is connected to the upper terminal of resistance II: and the control electrode oi tube I0 is connected to the upper terminal of resistance IIZ. Accordingly, the potential drop produced across resistance II! by the output current flow from tube 91 is utilized to control the conductivity of tube 12, and the potential drop produced across resistance I I2 by the output current flow from tube 00 is utilized to control the conductivity of tube I0.

Upon unbalance of the bridge network 2, for example, when the direction of unbalance is such that the alternating voltage impressed on the control electrodes oi triodes 90 and 91 from the output stage of the pre-amplifier drives the said control electrodes less negative or even positive during the half cycle of the supply line voltage that the anode of triode 96 is positive and the anode of triode 91 is negative, the conductivity of triode 96 will be increased while that of triode 91 will be decreased. The pulsating potential drop produced across resistance II 2 will then exceed that across resistance H3, and hence, tube I3 will be rendered more conductive than tube I2 to eflect energizati'on of motor I4 for rotation.

The increased current flow through triode 90 will produce a gradual increase in the potential drop across resistance 99 and condenser I00, and hence, a gradual reduction in the anode voltage applied to triode 96. Conversely, the decreased current flow through triode 91 will cause a gradual decrease in the potential drop across resistance I03 and condenser I04 and a consequent gradual increase in the anode voltage applied to triode 91. This operation, similarly to that of Fig. 6, causes a decrease in the amplification 'provided by triode 96 and an increase in the amplification provided by triode 91. Consequently, before the bridge network 2 has been rebalanced the pulsating potential drop produced across resistance H3 is made equal to or greater than that across resistance II! to effect premature deenergization of motor I4 for rotation or reversal in its energization as required to compensate for the inertia of the motor and the associated rebalancing mechanism.

Fig. 8 illustrates a modified arrangement of the Fig. 7 disclosure wherein the parallel connected resistance 99 and condenser I00 and the parallel connected resistance I03 and condenser I04 have been eliminated, and the premature deenergization and reversal in the energization of motor I4 are obtained by means of a condenser II4 connected between the upper terminals of resistances II2 and H3. With this arrangement, upon sustained unbalance of bridge network 2, delayed recovery in the biasing potentials produced across resistances II: and H3 is caused by condenser II4 to cheat premature deenergization or reversal in the energization of motor I4, as the alternating voltage impressed on the input circuits of triodes 00 and 01 from the preamplifier output stage decreases and thereby to prevent overshooting and consequent hunting or the bridge rebalancing-contact I! about the balancing point.

' Fig. 9 illustrates a modification oi the embodiment of my invention shown in Fig. 8 in which a single time delay or damping condenser fla is employed in lieu oi the parallel connected re.- sistance 00 and condenser I00 in the anode circuit of triode 00 and the parallel connected resistance I00 and condenser I04 in the anode circuit of triode 01. Condenser 01a is connected directly between the cathode of tubes 00 and' 91 and operates, in conjunction with resistances MI and I00, upon sustained unbalance oi the bridge network 2 to cause a delayed decrease in the conductance oi the tube I! or II whose conductivity was increased as a result of bridge unbalance and to cause a delayed increase in the conductance of the other tube. -In this arrangement, as the rebalancing action 01! the reversible motor I4 and the associated rebalancing structure decreases the unbalance oi the bridge network 2, delayed recovery in the biasing potentials across resistances IOI and I0! is caused by the condenser 01a to produce premature restoration of the conductances of tubes I2 and II, or even reversal in those conductive relations, and thereby a positive and powerful damping action on the operation 01' motor I4.

It lSIl'ltEd that the tubes I2 and II in the arrangement of Fig. 9 may either be of the type which cut off when the potentials of the control electrodes are the same as their associated cathodes or may be of the type requiring a negative potential on'the control electrodes relatively to the potentials of the associated cathodes to cut off their conduction. When the direction of bridge network unbalance is such as to cause the triode 95 to become more conductive than the triode 91, and hence, to cause the control electrode of tube "3 to be driven positive with respect to its associated cathode to cause energization of motor It for rotation in one direction, a charge is stored on condenser 01a during the half cycle that triode 96 is conductive which dissipates itself during the next hali cycle through resistances IOI and I05. During this latter half cycle triode 9'! tends to conduct but its conductivity is reduced by the alternating potential impressed on its control electrode as a result of the bridge network unbalance. The direction of the condenser discharge current through resistance I05 for the condition of unbalance under consideration, is such as to render the lower end of resistance I00 positive with respect to the potential of the upper terminal, and hence, to apply a negative potential to the control electrode of tube 12 which tends to cut off the conduction of this tube even though it is of the type requiring a negative potential on the control electrode to produce cut oil.

The modification of Fig. 10 differs in arrangement from that of Fig. 6 in that a parallel connected resistance H5 and a condenser II6 are connected in the cathode circuit of triode 06 and a resistance III and condenser IIO are connected in the cathode circuit of triode 91 for obtaining the desired hunting elimination in the motor operation in place of the parallel connected resistance and condenser 90 and the parallel connected resistance I03 and condenser I04. In addition, the cathode biasing resistance IIII of Fig. 6 has been eliminated in this modification, being replaced partially by the resistance I II and asaaou I I6 and I I1, I II in the respective cathode circuits of triodes 96 and 91 operates to cause a change i one direction in the amplification oi triode 96 upon sustained bridge unbalance by changing in a corresponding direction the bias voltage impressed on the control electrode of triode 96, and to simultaneously cause a change in the opposite direction in the amplification of triode 91 by correspondingly changing the bias voltage impressed on the control electrode of triode 91. Otherwise the operation of this modification of my invention is like that of Fig. 6, and therefore, further explanation of this modification is unnecessary.

The modification of Fig. 11 differs from the arrangement shown in Fig. in that a single condenser I2I in conjunction with the cathode biasing resistances IIII and I05 provide the desired anti-hunting action and, therefore, replace the resistances H5, H1, H9 and I and the condensers H6 and I I6 of Fig. 10. As shown, the condenser I2I is connected between the cathodes of the triodes 96 and 91. In Fig. 11, the output circuits of the triodes 96 and 91 have a common return circuit to the center tap of the transformer secondary winding 98 comprising the conductor I92 in which a resistance I22 is inserted. The resistance I22 constitutes a coupling resistance for coupling the output circuits of the triodes 96 and 91 to the parallel connected input circuits of the motor drive tubes 12 and 13. This coupling circuit includes a condenser I23 which is connected between a contact I24 in engagement with resistance I22 and the control electrodes of tubes 12 and 13. If desired, additional stages of ampliilcation may be provided between the coupling resistance I22 and the input circuit of triodes 12 and 13. The control electrodes 12 and 13 are connected by means of a fixed resistance I25 to the grounded conductor 65. The contact I24 in engagement with the resistance I22 is preferably slideable along the length of the latter and is provided for varying the sensitivity of the apparatus.

In the operation of this modification of my invention an increase occurs in the bias voltage impressed on the control electrode of the triode 96 or 91 whose conductance is increased as a result of unbalance of the bridge network 2 and a simultaneous decrease occurs in the bias on the control electrode of the other triode 96 or 91.

This change in the bias voltages impressed on the control electrodes of the triodes 96 and 91 operates to change the amplification provided by these triodes so that when the alternating voltage impressed on the control electrodes of triodes 96 and 91 decreases as the bridge network 2 is being rebalanced, the conductivities of the two triodes wil be rendered exactly equal or their conductive relations will be reversed before the rebalancing action of the bridge network 2 is completed, thus providing compensation for the inertia of the motor and the associated rebalancing structure. In other words, as the rebalancing action reduces the alternating voltage impressed on the control electrodes of triodes 96 and 91, delayed recovery in the biasing voltages applied to the said control 18 electrodes due to the action of condenser I2I causes premature restoration of the triode conductances to equality or even reversal in the conductive relations, thus effecting a positive and powerful damping action on the operation oi the motor I4. I

,, The modification at Fig. 12 difiers from the arrangement of Fig. 6 in that two series connected resistances I26 and I21 are connected in the cathode circuit of triode 96 in lieu of the resistance IOI an two series connected resistances I29 and I29 are connected in the cathode circuit of triode 91 in lieu of the resistance I65. A center tapped resistance I36 is connected between the point of connection of resistances I26 and I21 and the point of connection of resistances I26 and I49. The center tap on resistance I30 is connected to the grounded conductor 65. A resistance I3I is connected between the control electrode of the motor drive tube 12 and a conductor I32 which is connected to the lower terminals of resistances I66, I21 and I29 and also is connected to the center tap on the transformer secondary winding 98. Similarly, a resistance I33 is connected between the control electrode or the motor drive tube 13v and the conductor I32.

Compensation for the inertia of the reversible electrical motor I4 and the associated bridge rebalancing mechanism is obtained in Fig. 12 by mzans of the delaying action of a parallel connected resistance I34 and a condenser I35 which are connected between the cathode of triode 96 and the control electrode of tube 12 in conjunction with resistance I3I, and by means of a parallel connected resistance I36 and a condenser I31 which are connected between the oathode of triode 91 and the control electrode of tube 13 in conjunction with resistance I33.

The manner in which the desirable damping of motor I4 is accomplished by the modification cf Fig. 12 will now be explained. On the assumption that the direction of the bridge network unbalance is such as to cause the application of an alternating voltage to the control electrodes of triodes 96 and 91 of the proper phase to cause an increase in the conductance of triode 96 and a decrease in the conductance of the triode 91, an increase in potential drop will be produced across the resistances I26 and I21 while a decrease in potential drop will be produced across the resistances I28 and I29. The increase in potential drop across resistances I26 and I21 will be immediately transmitted by the parallel connected resistance I34 and condenser I35 to the control electrode of the tube 12 to cause an increase in the conductivity of the latter. Simultaneously, the decrease in potential drop across the resistances I28 and I29 will be transmitted by the parallel connected resistance I36 and condenser I31 to the control electrode of tube 13 to cause a decrease iri the conductance of the latter. In this manner, the motor I4 will be selectively energized for rotation in the proper direction to effect rebalance of the bridge network.

As the rebalancing action proceeds, a. current flow will be established from the upper end of resistance I26 through the resistance I34 and resistance I3I and through the conductor I32 to the lower end of resistance I21. This current flow will establish a potential drop across the resistance I34 which will have the effect oi! causing the potential of the control electrode of tube 12 to be driven less positive. Simultaneously, there will be a decrease in the current flow through the 19 1 resistance I35, and accordingly, the potential of the control electrode of tube I3 will be rendered may even be energized for rotation in the reverse direction before the bridge network 2 is rebalanced. In this manner, precise compensation for the inertia of the rebalancing motor and the associated bridge rebalancing structure may be obtained thus eliminating or at least minimizing the tendency for the motor drive system to overshoot the balance point and to hunt.

In the modifications of my invention shown in Figs. 1 and 3 through 12, the controlling voltage for selectively actuating the reversible electrical motor I4 for rotation in one direction or the other is alternating in character and is of the same frequency as that supplied by the-mains 4 and 5. In Fig. 13, I have illustrated another type 01' self-balancing electrical network in which my invention may advantageously be incorporated and in which the controlling voltage for effecting selective energization of the reversible motor I4 for rotation in one direction or the other is a unidirectional voltage. Specifically, the controlling voltage is that produced across a resistance I38 and is variable in magnitude in accordance with the changes in a variable condition to be measured. The manner in which a variable unidirectional voltage is produced across resistance I38 is immaterial for the purposes of the present invention. Merely by way of example, however, it may be produced by a direct current flow through resistance I38 from conductors I38 and I40 which may be connected in the output circuit of a photoelectric pyrometer oi. the type disclosed in Fig 1 of the J. T. Nichols Patent 2,241,557, which was issued on May 13, 1941, from an application filed July 25, 1936.

The variable unidirectional voltage drop produced across the resistance I38 i impressed on the input circuit of a triode I having anode, control electrode, cathode and heater filament elements. Triode I4I comprises one triode of a twin tube which contains a second triode I42 which may be identical to the triode MI. The input circuit for the triode I 4i may be traced from the control electrode through resistance I38, 8. slidewire resistance I43, a contact I44 which is in slideable engagement with resistance I43, and a cathode biasing resistance I45 to the cathode of triode I. The input circuit of triode I42 may be traced from the control electrode through the cathode biasing resistance I45 to the cathode of triode I42.

Energizing voltage is supplied the heater filaments of triodes HI and I42 from the secondary winding I48 of a transformer 430 having a line voltage primary winding 44 and secondary windings 48 and I" in addition to the secondary winding I46.

A unidirectional current flow is established through the slidewire resistance I43 by a full wave rectifier and filter arrangement generally designated by the reference character I48 which receives energizing current through supply conductors I49 and I50 from the supply conductors 4 sistanc I43 are connected to the output terminala lli'and I52 0! the filter I48. The polarity oi theterminal III ispositive with respecttomat of terminal I52, and hence, the potential oi the upper terminal of resistance I43 is rendered positive with respect to the lower terminal when the variable potential drop under measurement produced across resistance I33 is of the polarity indicated. The sliding contact I44 inengagement with resistance I43 is arranged to be adjusted along the length of resistance I43 by the reversible electrical motor I4. Preferably, the slldewire resistance I43 and contact I44 are arranged in cooperative relation with a recorder chart and recording mechanism as is shown in Fig. 2 to provide a record oi the variations in voltage across resistance I33.

Anode voltage is supplied to triodes III and I42 from the full wave rectifier and filter I48. Specifically, the anode circuit of triode I may be traced from the positive terminal I53 0! the rectifier and filter I48 through a conductor I54, a resistance I55, a parallel connected resistance I55 and condenser I5I to the anode of triode I, the cathode, the cathode biasing resistance I45 and a conductor I58 to the negative terminal I33 oi the rectifier and filter I48. 3 The anode clrcuit oi. triode I42 may be traced from the positive terminal I53 through conductor I54, a resistance I68, a parallel connected resistance III and condenser I62 to the anode of triode I42, the cathode, the cathode biasing resistance I45 and the conductor I53 to the negative terminal I53.

The potential drop produced across resistance I55 by the anode current flow through the triode I is impressed on the input circuit oi triode l2 and the potential drop produced across the resistance I53 by the anode current fiow of triode I42 is impressed on the input circuit of triode I3. Specifically, the cathodes of triodes I2 and "I3 are connected to the upper ends of resistances I55 and I58, the control electrode of triode I2 is connected to the lower end of resistance I55, and the control electrode of triode I3 is connected to the lower end of resistance I". The triodes I2 and I3 correspond to the triodes 12 and I3 oi the previously described modifications of my invention and receive anode energizing voltage from the transformer secondary winding 45 and are arranged to eilect selective actuation oi the motor control winding 39 with pulsating current which leads or lags by approximately the voltage of the alternating supply mains 4 and 5 when one or the other oi the triodes I2 and I3 is rendered more conductive than the other.

In the balanced condition oi the arrangement of Fig. 13, the sliding contact I44 will assume such a position along the length of resistance I43 that the potential drop across resistance I 43 tapped oil by the contact I44 is exactly equal and opposite to the potential drop produced across the resistance I38. With such adjustment, the control electrode of triode I" will be at the potential of the lower or negative end of cathode biasing resistance I45, as will also the control electrode of triode I42. The anode current ilow through the resistance I55 will then be exactly the same as that through the resistance I38, and consequently, the control electrode of triode I2 will be at the same potential as that 0! triode 13. Under this condition, the conductivity oi triode 12 is exactly the same as that or triode I3, and hence, motor I4 will not be energized for rotation in either direction relatively to that of its associated cathode, the condenser I82 delays recovery of the potential drop across resistance I i to its original value, and therefore, tends to maintain the amplification of the triode I42 at an increased value at the same time that the condenser IBI tends to maintain effectuate energization' of motor I4 for rotation.

The direction of rotation of motor I4 will be such as to cause movement of the sliding contact I44 in the upward direction to counteract the increased potential produced across resistance I38.

Upon sustained unbalance in the opposed potential drops across resistances I3. and I43, the condenser I51 in the anode circuit of triode I will gradually charge to cause an increase in the voltage drop across the resistance I55. This increased potential drop across resistance I5 effectively decreases the anode voltage applied to triode HI, and therefore, causes a reduction in the amplification which is provided by the triode Thus, upon unbalance, the amplification provided by triode I4I for the case considered is rendered less than that of triode I42. As the potential of thecontrol electrode of triode I4l relatively to the potential of the associated cathode is gradually restored to its original value due to adjustment of contact I44 along slidewire resistance I43, delayed recovery in the potential drop across resistance I55 to its original value causes the amplification of triode I to temporarily remain at such decreased value with the result that the potential drop across resistance I55 will be restored to equality with the voltage drop across resistance I60 before the adjustment of the contact I44 to the new balanced position has been completed. Restoration of the potential drops across resistances I55 and I60 causes deenergization of motor I4 for rotation. Thus, the motor I4 is prematurely deenergized for rotation as a result of the action of the parallel connected resistance I55 and condenser I51. choice of the circuit components, the potential drop across resistance I55 may even become less than that across resistance I50 before the adjustment of contact I44'is completed to thereby effectuate energization of reversible motor I4 for rotation in the reverse direction.

The aforementioned damping action is further enhanced by the operation of the resistance I6I and condenser I62 in'the anode circuit of triode I42. increased, the bias voltage produced across resistance I45 is increased to cause the potential of the control electrode of triode I42 to be rendered more negative with respect to the potential of the associated cathode. Consequently, upon increase in the conductivity of triode I the conductivity of triode M2 will be decreased. Decrease in the conductivity of triode I42 will cause a decrease in the current flow through resistances I60 and IIiI and, therefore, will cause an increase in the conductivity of the triode 11. Such increase in conductivity of triode I3 is in the proper direction to produce a greater energizing current flow to motor I4 for rotation in the direction of rotation. The decrease in potential drop across resistance I6I causes a greater anode voltage to be applied to the anode of the triode I42 and therefore provides greater amplification from the triode I42. While the potential of the control electrode I is being restored to its original value By proper When the conductivity of triode MI is the amplification of triode I4I- at a decreased value. These two eifects combine to effect premature deenergization of motor I4 for rotation and if desired actual energization of the motor for rotation in the reversed direction to quickly bring the motor to a stop and prevent overshooting and consequent hunting.

Subject matter disclosed but not claimed hereinis disclosed and claimed in a divisional application filed May 1, 1947, Serial No. 745,308, which issued as Patent No. 2,449,476 on September While in accordance with the provisions of the statutes, I have illustrated and described the best forms of my invention now known to me, it will be apparent to those skilled in the art that changes in the form of the embodiments of my invention illustrated and described herein may be made without departing from the spirit of the invention as set forth in the appended claims. It will be understood also that use may sometimes be advantageously made of some features of my invention without a corresponding use of other features.

Having now described my invention, what I claim as-new and desire to secure by Letters Patent is as follows:

1. An electrical network including a pair of electronic valves each having an input circuit and having normally equally conductive output circuits connected in opposite phase relation to an alternating current supply source, means to impress a variable controlling voltage on at least one ill of said input circuits to vary the conductivity of the corresponding one of said valves with respect to the conductivity of the other of said valves, means to adjust .the voltages impressed on said input circuits as required to restore equality in the conductivities of said valves, electrical reactance means connected in both the input and output circuits of said valves and operative prior to completion of the adjustment by said last mentioned means to restore equality in the conductivities of said valves, and a motor having a winding coupled to said output circuits.

2. A motor control apparatus for use with an alternating current supply source providing alternating current of predetermined frequency, including a pair of electronic valves having normally equally conductive output circuits connected in opposite phase relation to said alternating current supply source and having input circuits to which a variable controlling voltage is coupled in substantially unmodified form to increase the conductivity of one of said valves above that. of the other of said valves, electrical reactance means connected in both the input and output circuits of said valves and operative upon decrease in said controlling voltage to reverse the conductive relations of said valves before said controlling voltage is reduced to zero, and an alternating current motor having a winding coupled to said output circuits and a winding adapted to be coupled to said alternating current source. I

3. A motor control apparatus for use with analternating current supply source providing alternating current of predetermined frequency, including a pair of electronic valves having norasaaou I 23 mally equally conductive output circuits connected in opposite phase relation to said alternating current supply source and having input circuits to which a variable controlling voltage is adapted to be coupled to increase the conductivity of one of said valves above that of the other of said valves, means to couple said controlling voltage in substantially unmodified form to said input circuits, said coupling means ineluding electrical reactance means operative upon decrease in said controlling voltage to first restore equality in the conductivities of said valves and then to increase the conductivity of said other valve above that of said one valve before said controlling voltage is reduced to zero, and an alternating current motor having a winding coupled to said output circuits and a winding adapted to be coupled to said alternating current source.

4. A motor control apparatus for use with an alternating current supply source providing alternating current of predetermined frequency, including a pair of electronic valves having normally equally conductive output circuits connected in opposite phase relation to said alternating current supply source and having input circuits to which is coupled a variable controlling voltage having an alternating component of said predetermined frequency which is substantially in phase with or substantially 180 out -of phase with the alternating current of said source to increase the conductivity of one of said valves above that of the other of said valves, electrical reactance means connected in both the input and output circuits of said valves and operative upon decrease in said controlling voltage to reverse the conductive relations of said valves before said controlling voltage is reduced to Zero, and an alternating current motor having a winding coupled to said output circuits and a winding adapted to be coupled to said alternating current source.

5. A motor control apparatus including an alternating current supply source providing alternating current of predetermined frequency, a pair of electronic valves having output circuits con nected in opposite phase relation to said alternating current supply source and having input circuits upon which a controlling voltage having an alternating component of said predetermined frequency is adapted to be impressed to increase the conductivity of one ofsaid valves and to decrease the conductivity of the other of said valves, time delay means connected in said input and output circuits and operative when one of said valves becomes more conductive than the other to decrease the amplification provided by the electronic valve the conductivity of which is 'increased, and an alternating current motor having a winding coupled to said output circuit and a winding coupled to said alternating current source.

.or 180 out of phase with said alternating current is adapted to be impressed to increase the conductivity of one of said valves and to decrease the conductivity of the other of said valves, re-

sistanoe means connected in said input and out creased, capacitance mean associated with said resistance means to delay the effects of the latter on the amplification provided by said last mentioned electronic valve, and an alternating current motor having a winding coupled to said output circuits'and a winding coupled to said alternating current source.

7. A motor control apparatus including an alternating current supply source providing alternating current of predetermined frequency, a pair of electronic valves having output circuits connected in opposite phase relation to said alternating current supply source and having input circuits upon which a controlling voltage having an alternating component of said predetermined frequency which is substantially in phase with or 180 out of phase with said alternating current is adapted to be impressed to increase the conductivity of one of said valves and to decrease the conductivity of the other of said valves, a parallel connected resistance and capacitance connected in each of said output circuits to decrease the amplification provided by the electronic valve the conductivity of which is increased, and an alternating current motor having a winding coupled to said output circuits and a, winding coupled to said alternating current source.

8. A motor control apparatus including an alternating current supply source providing alternating current of predetermined frequency, a pair of electronic valves having output circuits connected in opposite phase relation to said alternating current supply source and having input circuits upon which a controlling voltage hav ing an alternating component of said predetermined frequency which is substantially in phase with or 180 out of phase with said alternating component is adaptedto be impressed to increase the conductivity of the other of said valves, means in said input circuits to produce biasing voltages which are oppositvely variable from a normal value in one direction or the other and l to an extent depending upon the phase and amplitude respectively of said alternating component of voltage, means to delay changes in said biasing voltages, and an alternating current motor having a winding coupled to said output circuits and a winding coupled to said alternating current source.

9. Means to control the operation of a reversible electrical motor for rotation in one direction or the other in accordance with the phase and amplitude of a controlling alternating voltage of predetermined frequency including an alternating current supply source providing alternating current of said predetermined frequency, a pair of electronic valves having output circuits connected in opposite phase relation to said alternating current supply source and having input circuits upon which said controlling alternating voltage is impressed to increase the conductivity of one of said valves andto decrease the conductivity of the other of said valves, time delay means connected in said input and output circuits and operative when one of said valves becomes more conductive than the other to decrease the amplification provided by the electronic valve the conductivity of which is increased, and an alternating current motor to be controlled having nating current supply source providing alternating current of said frequency, said controlling alternating voltage being substantially in phase with or 180 out of phase with the alternating current of said source, a pair of electronic valves having output circuits connected in oppositephase relation to said alternating currentsupply source and having input circuits upon which said controlling alternating voltage is impressed to increase the conductivity of one of said valves and to decrease the conductivity of the other of said valves, resistance means connected in said input and output circuits and operative when one of said valves becomes more conductive than the other to decrease the amplification provided by the electronic valve the conductivity of which is increased, capacitance means associated with said resistance means to delay the effects of the latter on the amplification provided by the last mentioned electronic valve, and an'alternating current motor to be controlled having a-winding coupled to said output circuits and a winding coupled to said alternating current source.

ll. Means to control the operation of a reversible electrical motor for rotation in one direction or the other in accordance with the phase and amplitude of a controlling alternating voltage of predetermined frequency including adjustable means to create and to regulate the amplitude of said controlling alternating voltage, an alternating current supply source providing alternating current of said predetermined frequency, said controlling alternating voltage being substantially in phase with or 180 out of phase with the alternating current of said source, a palrof electronic valves having output circuits connected in opposite phase relation to said alternating current source and having input circuits upon which said controlling alternating voltage is impressed to increase the conductivity of one of said valves and to decrease the conductivity of the other of said valves, resistance means connected in each of said output circuits to decrease the amplification provided by the electronic valve the conductivity of which is increased, capacitance means associated with said resistance means to delay the effects of the said resistance means on the amplification provided by the last mentioned electronic valve, and an alternating current motor having a winding coupled to said output circuits and a winding coupled to said alternatingcurrent source to adjust said adjustable means to reduce the amplitude of said controlling alternating voltage.

12. Means to control the operation of a reversible electrical motor for rotation in one direction or the other in accordance with the phase and amplitude of a controlling alternating voltage of predetermined frequency including adjustable means to creat and to regulate the amplitude of said controlling alternating voltage, an alternating current supply source providing alternating current of said predetermined frequency, said controlling alternating voltage being substantiallyin phase with or 180 out of phase withthe alternating current of said source, a pair of electronic valves having output circuits connected in opposite phase relation to said alternating current source and having input circuits upon which said controlling alternating voltage is impressed, a parallel connected resistance and capacitance connected in each of said output circuits to decrease the amplification provided by the electronic valve the conductivity of which is increased as a result of application of said controlling alternating voltage to said input circuits, and analternating current motor having a winding coupled to said output circuits and a winding coupled to said alternating current source to adjust said adjustable means to reduce the amplitude of said controlling alternating voltage.

13. Means to control the operation of a reversible electrical motor for rotation in one direction or the other in accordance with th phase and amplitude of a controlling alternating voltage of predetermined frequency including adjustable means to create and to regulate the amplitude of said controlling alternating voltage, an alternating current supply source providing alternating current of said predetermined frequency, said controlling alternating voltage being substantially in phase with or out of phase with the alternating current of said source, a air of electronic valves having output circuits connected in opposite phase relation to said alternating current source and having input circuits upon which said controlling alternating voltage is impressed, means in said input circuits to produce biasing voltages which are oppositely variable from a normal value in one direction or the other and to an extent depending upon the phase and amplitude respectively of said controlling alternating voltage, means to delay changes in said biasing voltages, and an alternating current motor having a winding coupled to said output circuits and a winding coupled to said alternating current source to adjust said adjustable means to reduce the amplitude of said controlling alternating voltage.

14. Means to control the operation of a reversible electrical motor for rotation in one direction or the other in accordance with the phase and amplitude of a controlling alternating voltage of predetermined frequency including adjustable means to create and to regulate the amplitude of said controlling alternating voltage, terminals to which an alternating current supply source providing alternating current of said predetermined frequency is adapted to be connected, said controlling alternating voltage being substantially in phase with or 180 out of phase with the alternating current of said source, a transformer having a primary winding connected to said source of alternating current and having a center tapped secondary winding, 9. pair of electronic valves each having an anode, a cathode and a control electrode, means to impress said controlling alternating voltage between said cathodes and controlelectrodes, a connection from one end of said transformer secondary winding to the anode of one of said valves, a connection from the other end of said secondary winding to the anode of the other of said valves, an alternating current motor to adjust said adjustable means to reduce the amplitude of said controlling alternating voltage and having two windings one of which is connected to said terminals, 9. parallel connected resistance and capacitance connected between each of the cathodes of said valves and one end of the other of said motor winding, and a connection from the a,sas,oss

other end of said other motor winding to the center tap on said transformer secondary winding.

15. Means to control the operation 01 a reversible electrical motor for rotation in one direction or the other in accordance with the phase and amplitude of a controlling alternating voltage of predetermined frequency including adjustable means to create and to regulate the amplitude of said controlling alternating voltage, terminals to which an alternating current supply source providing alternating current of said predetermined frequency is adapted to be connected, said controlling alternating voltage being substantially in phase with or 180 out or phase with the alternating current or said source, a transformer having a primary winding connected to said terminals and thereby adapted to beconnected to said source of alternating current and having a center tapped secondary winding, a pair oi! elec tronic valves each having an anode, a cathode and a control electrode, means to impress said controlling alternating voltage between said con- I trol electrodes and cathodes, a parallel connected resistance and capacitance connected between one end of said secondary winding and the anode of one of said valves, a parallel connected resistance and capacitance connected between the other end oi! said secondary winding and the anode of the other of said valves, an output resistance connected between each of the cathodes means difierentially coupling the other of said motor windings to said output resistances.

16. Means to control the operation of a reversible electrical motor for rotation in one direction or the other in accordance with the phase and amplitude of a controlling alternating voltage of predetermined frequency including adjustable means to create and to regulate the amplitude of said controlling alternating voltage, terminals to which an alternating current supply source providing alternating current of said predetermined frequency is adapted to be connected, said controlling alternating voltage being substantially in phase with or 180 out of phase with the alternating current of said source, a transformer having a primary winding connected to said terminals and having a center tapped secondary winding, a pair of electronic valves having an anode, a cathode and a control electrode, means to impress said controlling alternating voltage between said control electrodes and cathodes, a connection between one end of said secondary winding and the anode of one of said valves, a connection between the other end of said secondary winding and the anode or the other of said valves, an output resistance connected between each of the cathodes of said valves and the center tap on said secondary winding, a condenser connected between said cathodes, an alternating current motor to adjust said adjustable means having two windings one of which is connected to said terminals, and means diiierentially couplingthe other of said motor windings to said output resistances.

17. An electrical network including a pair of electronic valves each having an input circuit and having normally equally conductive output circuits connected in opposite phase relation to an alternating current supply source, means to impress a variable controlling voltage on at least one of said input circuits to vary the conductivity of the corresponding one-oi said valves with respect to the conductivity of the other of said valves, means responsive to the relative conductivities of said valves to adjust the voltage impressed on said input circuits as required to restore equality in the conductivities of said valves,

and electrical reactan'ce means connected in both the input and output circuits Of said valves and operative prior to completion or the adjustment by said last mentioned means to restore equality in the conductivities of said valves.

- THOMAS R. HARRISON.

REFERENCES CITED The following references are of record in the ille of this patent:

' UNITED STATES PATENTS 

